This invention relates generally to magnetic resonance imaging (MRI). More specifically, the invention relates to a rotating anode x-ray tube for MRI.
A simplified diagram of a rotating anode x-ray tube used in the prior art is shown in FIG. 1. The rotating anode x-ray tube 100 comprises a housing 104, a glass envelope 108 for maintaining a vacuum around the cathode and anode, insulating oil 112, a cathode and focusing cup 116, a target 120, an anode 124, an x-ray window 128, a rotor 132, a stator 136, and expansion bellows 140. During conventional use the tungsten wire filaments held in the focusing cup are heated to ˜2200° C. causing electrons to be boiled off the wire surface by the process of thermionic emission. The large potential difference (on the order of 100 kV) between the cathode and anode causes the high-energy electrons that are boiled off the tungsten wire to accelerate towards and bombard the anode creating x-rays. Due to the inefficiency of this process, less than 1% of the electron beam energy is converted to x-ray energy; a tremendous amount of heat is deposited on the anode. By rotating the anode during the exposure process, the deposited heat is spread out along the circumference of the anode, which increases the instantaneous heat loading capability of the x-ray tube thus enhancing the x-ray output relative to a static anode.